Support for National has fallen by 6 points, and being topped by support for a Labour/Greens alliance which is up by 8 points, according to the latest Roy Morgan Poll.
The poll of almost 900 people suggests that an election result would be too close to call if voters now headed to polling booths.
44.5 percent of respondents said they supported National.
This is just behind a Labour/Greens alliance, which has 46 percent support.
Support for National's support partners has changed little - the Maori Party is unchanged on 1.5 percent, and Act is also unchanged on half a percent.
United Future has lifted from its previous zero rating to half a percent support.
Labour registered 31 percent which is up four points, the Greens are also up four points to 15 percent, while New Zealand First has fallen 2.5 points to 5.5 percent support.
The polling was done with both landline and mobile telephones across New Zealand this month.